Drug giant Allergan announced Monday the $2.5 billion acquisition of Zeltiq Aesthetics, makers of a fast-growing technology to eliminate body fat through "CoolSculpting," which essentially freezes unwanted fat away.

The patented cooling permits patients to experience "body contouring" without surgery. The venture represents a "$4 billion market opportunity worldwide and growing," according to Allergan, which is headquartered in Ireland.

The California-based company's process—"Cryolipolysis"—applies intense cold to an area, creating a sensation of numbness in the patient. The procedure involves no needles and allows patients to begin observing changes after three weeks, according to literature.

"By adding the best-in-class body contouring CoolSculpting System to our best-in-class facial aesthetics, and regenerative medicine offerings we are creating a world-class aesthetics business," said Brent Saunders, of Allergan, which also owns the anti-wrinkling injection technology.

The transaction must be approved by Zeltiq shareholders and is subject to regulatory review.

Shares of Zeltiq jumped 12.8 percent to $55.70, while Allergan rose 0.9 percent to 248.55 in midday trading.